Diesel engines pose particular problems when operated in an atmosphere or environment containing a fuel, such as, natural gas. This often occurs in oil fields where engines operating in and around oil or gas wells may be exposed to substantial quantities of gas-filled air. The engine will tend to draw the fuel/air mixture into its intake or suction side and as a result cannot be controlled by the operator so as to avoid serious overrunning and damage to the engine.
Previous attempts have been made to position a butterfly or damper valve on the intake side of the engine upstream of the intercooler or turbine sections and in many cases has caused serious damage to the engine. As a result, certain engine manufacturers have refused to permit the positioning of air cutoff valves on the intake side. On the other hand, there has been insufficient space on the discharge side leading into the intake manifold for the cylinders to position either a butterfly or damper valve. Typically, the discharge tube leading into the manifold and cylinders is necessarily horn-shaped or curved and will not accommodate a pivotal type of valve plate arrangement within the passage. Furthermore, there are plurality of discharge tubes, each of which requires controlled shutoff in the cylinders; yet it has been found that blocking of the air flow through the discharge tubes leading directly into the cylinders is far preferable to previous designs intended to shut down the air ahead of the intercooler or suction portions. It is therefore proposed to provide a novel and efficient manner and mean for selectively shutting down air flow into the cylinders in the discharge tubes leading into the cylinders and in such a way as to be completely safe and reliable in operation.